Johannes Holtfreter (1901-1992)

Johannes Holtfreter made important discoveries about the properties of the
organizer discovered by
Hans Spemann. Although he spent much time away from the lab over many years, he was a productive researcher. His colleagues noted that the time he spent away helped revitalize his ideas. He is credited with the development of a balanced salt medium to allow embryos to develop; the discovery that dead
organizer tissue retains
inductive abilities; and the development of specification, competence, and distribution of
fate maps in the developing
frog embryo. He was the sole author on all but three of the more than sixty papers he published. Johannes Holtfreter was born on 9 January 1901 in Richtenberg, Germany. He was the middle of three children, the only boy, and grew up collecting and drawing butterflies and other animals in the surrounding area. When World War I began, his family moved to Strausland, Germany, to avoid the war.

From 1917 to 1919 Holtfreter studied natural science at the Universities of Rostok and Leipzig. In 1919 he was attracted by the possibility of studying under Franz Doflein, an eminent naturalist, and transferred to the
University of Freiburg. Doflein died prior to Holtfreter’s arrival and was replaced by
Hans Spemann. Holtfreter completed his PhD work in
Spemann’s lab on the development of the liver and pancreas of the
frog embryo. He commented that this work was not of great interest to himself or
Spemann.

Although Holtfreter was in
Spemann’s laboratory and shared a bench with
Hilde Mangold, he played no part in the discovery of the
organizer. He was described as a loner, worked at night, and disappeared for long periods of time to take hikes through the surrounding countryside. In 1924 Holtfreter received his PhD and left to study at the
Stazione Zoologica in Naples, Italy. While in Naples he decided to travel around Italy rather than study in the laboratory. He took up painting and writing and after two years returned to find no prospects for a research appointment. In 1928
Otto Mangold offered him a research position which Holtfreter accepted.

Under
Mangold, Holtfreter returned to
embryology and began to study aspects of the
organizer. He was presented with some technical challenges to embryo growth.
Frog embryos had trouble developing in hypotonic solutions like pond water, so he developed Holtfreter's medium, a balanced salt solution. In this solution a
frog embryo could develop for several weeks. Holtfreter was also challenged by bacterial infections so he introduced sterile conditions. With these modifications, he was able to produce many more successful embryos and transplantations than the original Spemann-Mangold experiments, in which only five of many hundreds of transplants survived. Holtfreter then began further experimentation on the
organizer. He wanted to test the capacity of the
organizer to induce a new body axis after it was “devitalized,” or killed. He froze, boiled, dried, and subjected
organizer tissue to alcohol, then transplanted it to a developing embryo. Each of the killed
organizers retained their capacity for
induction. Holtfreter demonstrated that the
organizer did not function based on its structure, but instead relied on chemical action.

Holtfreter then tested the inductive abilities of a variety of embryonic and adult tissues from various phyla. He discovered that they were all capable of
inducing neural tissue. By performing a purification on the
organizer tissue, he also discovered two types of
organizer, one a neural inducer and the other a mesodermal inducer. In 1934 Holtfreter accepted a position at the
University of Munich where he studied small pieces of gastrula stage embryos. There he developed an early
fate map based on the observations of embryonic tissues in the absence of influences from other tissues. He also continued to study
induction and remained in contact with
Joseph Needham and
Conrad Hal Waddington, who were also studying
induction in other animals. In 1939 Holtfreter escaped Germany to England. In 1940 a German invasion of England seemed imminent, so he and other German refugees were interned in Canada for nearly two years. After his internment, he received a Rockefeller Fellowship to study at
McGill University in Canada. He spent the fellowship studying
gastrulation by observing cellular movements and established the current model of
gastrulation.

Holtfreter accepted an assistant professorship at the
University of Rochester in 1946 and was promoted to professor in 1948. In 1955 Holtfreter collaborated with
Viktor Hamburger to publish a chapter on
amphibian development. In that article he noted his disdain for gradients of signaling molecules and preferred cell to cell interactions for explanations of signaling.